'Empty Spam' and 'Empty Trash' comment buttons not displayed on mobile

[SergeyBiryukov]

Since [26134], top navigation for list tables is not displayed on mobile, which means that 'Empty Spam' and 'Empty Trash' buttons were only displayed in bottom navigation.

Since [40297], these buttons are not displayed in bottom navigation either (on both mobile and desktop) if there's only one page of comments in Spam/Trash, because $this->extra_items is empty, $this->items ends up empty too​ in ::display(), so $this->has_items() returns false.

The lack of the button also causes the %s items string to overlap with the search bar, see the screenshot.

If there are two or more pages of comments in Spam/Trash, the buttons are displayed as expected.

[SergeyBiryukov]

40975.patch​ fixes the issue by saving $this->has_items() to a static variable, so that the value is consistent between top and bottom navigation.

Other screens appear to be unaffected, as they don't reset $this->items before displaying bottom navigation.

[SergeyBiryukov]

In 41022:

Comments: In WP_Comments_List_Table::extra_tablenav(), save the state of ::has_items() to a static variable, so that the value is consistent between top and bottom navigation.

This prevents "Empty Spam" and "Empty Trash" buttons from disappearing if there's only one page of comments in Spam/Trash.

Fixes #40975.

[SergeyBiryukov]

In 41023:

Comments: In WP_Comments_List_Table::extra_tablenav(), save the state of ::has_items() to a static variable, so that the value is consistent between top and bottom navigation.

This prevents "Empty Spam" and "Empty Trash" buttons from disappearing if there's only one page of comments in Spam/Trash.

Fixes #40975.

Merges [41022] to the 4.8 branch.